This invention relates to a two-color printing thermal head capable of outputting appropriate, different heating temperatures at the same scanning time to a heat-sensitive substance for developing different colors in response to the heating temperatures, for example, and in particular to an art for giving high power a thermal head for high temperature and low power to a thermal head for low temperature for optimizing the print quality.
To print on heat-sensitive paper with a thermal head, in a related art, as shown in FIG. 8A, if print energy (temperature) is made higher than T0, printing is executed in a constant color, such as black, and if print energy is made lower than T0, the print density is reduced, thus the thermal head is not heated for a portion to be skipped in printing. That is, only operation control as to whether or not printing is to be executed depending on the presence or absence of data on one line is performed.
To perform this control, a thermal head provided with an additional history control circuit for limiting a temperature rise caused by heat accumulated in a thermal head substrate also exists for controlling the thermal head at a single temperature, namely, single energy in printing.
In recent years, multi-color heat-sensitive paper printed in black, for example, when printing is executed with a high-temperature thermal head and printed in red, for example, when printing is executed with a low-temperature thermal head has been manufactured. For example, it has been provided as product name MB-23 of Oji Paper Co. Ltd.(JP).
That is, thermal-sensitive paper of this kind develops red, for example, when the print energy (temperature) of a thermal head is T2 and black when the print energy of a thermal head is T1 (T2&lt;T1), as shown in FIG. 8B. If the print energy is made higher than T1, a whitening phenomenon appears. Thermal-sensitive paper of this kind is available not only with a combination of red and black, but also any other color combination based on low and high print energy.
By the way, when such multi-color heat-sensitive paper is used for executing multi-color printing, for example, red and black printing on a scanning line L0, as shown in FIG. 9A, with a thermal head in a related art, for example, first a red print data portion needs to be transferred in the current amount corresponding to a low temperature, then again data transfer needs to be executed on the same scanning line L0 in the current amount corresponding to a high temperature.
To execute two-color (red and black) printing as shown in FIG. 9B, likewise a red print data portion is transferred in the current amount corresponding to a low temperature on scanning lines L1, L2, . . . , then data transfer is executed on the same scanning lines L1, L2, . . . in the current amount corresponding to a high temperature.
Thus, to handle two types of energy, data transfer is executed twice on one line and each type of energy is set. Since it is necessary to execute data transfer twice on one line, a problem of low print speed is involved.
To solve this problem, a thermal head for making it possible to set different types of energy on one line in one scanning as shown in FIG. 10 is proposed in U.S. patent application Ser. No. 09/538,283 filed Mar. 30, 2000 (Japanese Patent Application No. Hei 9-302728).
By the way, a control circuit of the thermal head controls high-energy portion data and low-energy portion data separately. Thus, if two types of input energy data are mixed, printing of the low-energy data cannot be executed on low-energy print dots because of the effect of the high energy side, and the print result becomes close to the high-energy side data. For example, the portion to be printed in red is actually printed in a color close to black.
To overcome such a problem, a thermal head adapted so as not to affect printout of low-energy data in the present or absence of high-energy print data in the proximity of print points as shown in FIG. 11 is also proposed in the Japanese laid open Patent Publication no. 11-208008, filed Aug. 3, 1999 (Japanese Patent Application No. Hei 10-12320).
According to the thermal heads as proposed in the above-mentioned U.S. patent application, as high energy printing control and low energy printing control can be very precisely executed, two-color data can be precisely printed even if the two-color data are mixed.
For example, as shown in FIG. 9A, in case a black character area B and a red character area R are respectively blocked on paper, the black area and the red area can be also definitely printed by the control circuit shown in FIGS. 10 or 11. However, when a dot of the low energy part exists in a part adjacent to a dot of the high energy part and before and after the dot in case a black character on a red background is printed as shown in FIG. 9B, that is, in case a red area R and a black area B are mixed, there is a detect that as printing of a low energy part is developed in color close to printing of a high energy part by the printing of the high energy part, a character and a pattern become indefinite. However, according to the art described above, as a bad effect which high energy data has upon low energy data can be also effectively controlled in case plural types of input energy data are mixed as shown in FIG. 9B, clear and precise printing is also enabled in the case shown in FIG. 9B.
A rewritable print medium, such as an "Aladdin card" (registered trademark) manufactured by Tokyo Magnetic Printing Co. Ltd.(JP), is available. When high energy is given to the rewritable print medium by a thermal head, the medium is printable, but when low energy is given, change is made to a different color and characters, etc., printed on the medium by high energy are erased and characters, graphics, etc., can be again written on the medium by giving high energy.
The control circuits shown in FIGS. 10 and 11 can also be used for such a medium. In this case, a STROBE1 signal is set so as to add high energy for printing and a STROBE2 signal is set so as to give low energy for erasing print characters, etc. In this case, q1, q2, and q3 become print erasure data for performing print erasure control. For the medium, it is very strict to set the range of low energy for erasing characters, etc. Thus, preferably the heat history control based on the presence or absence of q2, q3 described above, namely, heating control based on the print erasure data q2, q3 as well as the magnitude of the STROBE2 signal is added for making energy adjustments.
Thus, the control circuits can also be used with the thermal head for the rewritable medium.
FIG. 12 is an equivalent circuit diagram to the control circuit in FIG. 11 and FIGS. 13A to 13E are logic tables of the control circuit shown in FIG. 12. In FIG. 11, the diode 23 and q2 input to the NAND circuit 19 have OR relation, thus are shown equivalently as an OR circuit 115 in FIG. 12A. The output protection circuit 13 in FIG. 11 is omitted in FIG. 12A. Thus, FIG. 11 can be represented equivalently by FIG. 12A.
In FIG. 12A, numeral 100 denotes an FET, numeral 101 denotes an OR circuit, numerals 102 and 103 denote multi-input AND circuits, numeral 104 denotes an AND circuit, numeral 105 denotes a multi-input AND circuit, numerals 106 and 107 denote AND circuits, numerals 108, 109, 110, 111, 112, 113, and 114 denote NAND circuits, numerals 115, 116, and 117 denote OR circuits, numerals 118, 119, 120, and 121 denote EOR circuits, and numerals 122, 123, 124, 125, 126, 127, 128, 129, and 130 denote inverters.
FIG. 12B (1), (2), and (3) summarize the unique control portion in the print control range (high energy part), the effect portion of high energy on the print control range (low energy part), and the unique control portion in the print control range (low energy part) shown in FIG. 12D. Q1, Q2, Q3, and Q4 in FIG. 12A denote latch data and q1, q2, and q3 also denote latch data.
For example, if the thermal head consists of 64 dots, 64 circuits in FIG. 12A are provided, and n of each of a terminal DOn, GQn, GAn, and GBn of the AND circuit 104, and Gqn of the multi-input AND circuit 105 indicates that a plurality of such circuits exist.
As shown in FIG. 13A, if STROBE q is "0" and latch data Q1 and q1 are "0" and "1" respectively as input and output of the multi-input AND circuit 105 (Gqn) is "1" as in-circuit output, the terminal DOn outputs ON regardless of whether STROBE Q is "1" or "0" and regardless of whether output of the AND circuit 104 (GQn) is "1" or "0." Asterisk * denotes either "0" or "1." If STROBE Q is "0" and STROBE q is "1" and latch data Q1 and q1 are "0" and "0" respectively, the terminal DOn outputs OFF regardless of whether output of the AND circuit 104 (GQn) is "1" or "0" and regardless of whether output of the multi-input AND circuit 105 (Gqn) is "1" or "0." In addition, the terminal DOn outputs ON or OFF in response to the "1" or "0" state of each of STROBE Q, STROBE q, Q1, q1, GQn, and Gqn shown in FIG. 13A.
The AND circuit 104 (GQn) outputs "1" or "0" in response to the "1" or "0" state of each of the AND circuit 106 (GAn) and the AND circuit 107 (GBn) as in-circuit output, as shown in FIG. 13B. The AND circuit 106 (GAn) outputs "1" or "0" in response to the "1" or "0" state of each of input GATE A1 and GATE A2 and latch data Q2 and LQ2, as shown in FIG. 13C.
The AND circuit 107 (GBn) outputs "1" or "0" in response to the "1" or "0" state of each of input. GATE B1 and GATE. B2 and latch data Q3 and RQ2, as shown in FIG. 13D.
The multi-input AND circuit 105 (Gqn) outputs "1" or "0" in response to the. "1" or "0" state of each of input GATE C1, GATE C2, and GATE C3 and latch data Q2 or q2, Q3 or q3, and LQ2 or RQ2, as shown in FIG. 13E.
By the way, with the thermal head in the related art shown in FIG. 10, FIG. 11, etc., the magnitude of print energy is set depending on the duration of applying the electric current flowing into the heating terminal. That is, it is determined by the magnitude of STROBE1, STROBE2 in FIG. 10, FIG. 11, and the current value, namely, unit power is the same.
Specifically, the heating value of the thermal head in unit time is made constant and large and small print energies are determined by the heating duration. That is, letting the heating value in the unit time be W, resistance of the thermal head be r0, and applied voltage be V, the heating value of the thermal head in the unit time, W, is determined as W=V.sup.2 /r. To use the thermal head in a high energy state, the thermal head is heated only for time t2, namely, by W.multidot.t2; to use the thermal head in a low energy state, the thermal head is heated only for time t1 (t2&gt;t1), namely, by W.multidot.t1.
That is, in the thermal head making it possible to set different large and small energies in one scanning based on the magnitude of a strobe signal described alter, the magnitude of the print energy (large or small) is set only based on the duration of heating the heater of the thermal head with the same heating value in the unit time applied.
Therefore, if the heating time is shortened to lessen the print energy, the heating value in the unit time is the same as that in the high energy state, thus insufficient color development may exist depending on the nature of heat-sensitive paper. When the thermal head is used with rewritable paper with characters, etc., printed in a high energy state, erased by giving low-energy heat from the thermal head is used, the characters cannot sufficiently be erased because of the short time in some cases.